1. Field of the Invention
The present invention relates to semiconductor structures and, more particularly, to a single-crystal silicon semiconductor structure.
2. Description of the Related Art
High precision analog circuits utilize semiconductor structures, such as resistors, which must be matched to a very high degree of accuracy. Current-generation photolithographic processes are extremely accurate, and can be used to form structures, such as polysilicon resistors, which are physically substantially identical to each other.
Although formed to be physically substantially identical to each other (in length, width, and height), polysilicon resistors often have resistances which fall within a wide range of values. This is because the resistance of a polysilicon resistor is strongly dependent on the grain structures within the polysilicon. The grain structures, however, are subject to a number of process variables, such as hydrogen content, which vary widely.
Thus, to have two polysilicon resistors which have equal resistances (values that fall within a very narrow range of values), the polysilicon resistors must be matched by laser trimming procedures which physically remove a portion of one of the polysilicon resistors until the resistive values of the two are equal (fall within the very narrow range of values).
Although the laser trimming process can provide polysilicon resistors which are substantially identical, the process is also time consuming and, thereby, expensive. Thus, there is a need for an approach to forming matched semiconductor resistors which does not require laser trimming.